• Proceedings of the Materials Research Society of Korea Conference
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• 2005.05a
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• pp.88-88
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• 2005

• Nuclear Engineering and Technology
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• v.52 no.2
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• pp.287-295
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• 2020

Group method of data handling (GMDH) is considered one of the earliest deep learning methods. Deep learning gained additional interest in today's applications due to its capability to handle complex and high dimensional problems. In this study, multi-layer GMDH networks are used to perform uncertainty quantification (UQ) and sensitivity analysis (SA) of nuclear reactor simulations. GMDH is utilized as a surrogate/metamodel to replace high fidelity computer models with cheap-to-evaluate surrogate models, which facilitate UQ and SA tasks (e.g. variance decomposition, uncertainty propagation, etc.). GMDH performance is validated through two UQ applications in reactor simulations: (1) low dimensional input space (two-phase flow in a reactor channel), and (2) high dimensional space (8-group homogenized cross-sections). In both applications, GMDH networks show very good performance with small mean absolute and squared errors as well as high accuracy in capturing the target variance. GMDH is utilized afterward to perform UQ tasks such as variance decomposition through Sobol indices, and GMDH-based uncertainty propagation with large number of samples. GMDH performance is also compared to other surrogates including Gaussian processes and polynomial chaos expansions. The comparison shows that GMDH has competitive performance with the other methods for the low dimensional problem, and reliable performance for the high dimensional problem.

• Journal of Astronomy and Space Sciences
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• v.34 no.4
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• pp.251-256
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• 2017

The electric coupling between the lithosphere and the ionosphere is examined. The electric field is considered as a timevarying irregular vertical Coulomb field presumably produced on the Earth's surface before an earthquake within its epicentral zone by some micro-processes in the lithosphere. It is shown that the Fourier component of this electric field with a frequency of 500 Hz and a horizontal scale-size of 100 km produces in the nighttime ionosphere of high and middle latitudes a transverse electric field with a magnitude of ~20 mV/m if the peak value of the amplitude of this Fourier component is just 30 V/m. The time-varying vertical Coulomb field with a frequency of 500 Hz penetrates from the ground into the ionosphere by a factor of ${\sim}7{\times}10^5$ more efficient than a time independent vertical electrostatic field of the same scale size. The transverse electric field with amplitude of 20 mV/m will cause perturbations in the nighttime F region electron density through heating the F region plasma resulting in a reduction of the downward plasma flux from the protonosphere and an excitation of acoustic gravity waves.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.519-520
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• 2006

Research was performed to increase the efficiency of a plasma reactor for $H_2$ yield. In the preceding studies $H_2$ was increased by adding Ni as a transitional metal catalyst and $TiO_2$ as a photocatalyst. In these experiments, it was found that distilled water, discharge frequency, and electrode configuration had a significant impact on $H_2$ generation. A substantial amount of hydrogen yield was observed at 2 kHz of discharge frequency and 12 kV of applied voltage. Within this favorable discharge conditions, the weight rate of $TiO_2$ and Ni powders was investigated. Plasma phenomenon was measured by electrical, optical and acoustical devices. It was found that emitted light, electric current and acoustical signals acquired from the discharge demonstrated systematical correlation. Changing the electrode's configuration allowed discharge distribution along the perimeter of the electrode's tip, which increased the density of streamers and plasma energy loadings, as the value of inception voltage for the discharge propagation decreased.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.3
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• pp.92-97
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• 2007

The overlay welding the automobile where the durability is demanded, it is used in the vessel engine valve, plant valve and pump parts. Cause of damage public opinion one what is thought is the fatigue load due to the opening and shutting operation right time repetition of the engine valve. The damage cause of the engine valve or explanation of destruction mechanism is very difficult. The research which it sees to make clear a overlay welding of Co-alloy by Plasma Transferred Arc Weld Surfacing Process reconsideration fatigue crack initiation and fatigue crack growth mechanism at high temperature.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.242-242
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• 1999

상대론적 전자빔 발생장치(300kV, 40kA, 60ns)를 통하여 발생하는 전자빔은 진공 중에서 공간전하한계전류값을 갖게 되어 진행이 어렵다. 이런 전자빔의 전파특성을 향상시키기 위하여 여러 가지 방법들이 실험되어졌다. 본 실험실에서 수행한 실험은 전자빔의 진행해나가는 도파관 속에 국부적인 plasma channel을 형성시키고 이에 따른 전자빔의 전파율의 향상을 유도하였다. 이때 형성되는 높은 에너지의 이온빔을 관찰하고 이온 전류밀도에 따른 전자빔의 수송효율사이의 관계를 관찰하였다. 전류밀도의 증가는 여러 가지로 응용 될 수 있다. 자유전자레이저(Free Electron Laser)는 microwave로부터 가시광선 영역을 포함해 X-ray 영역까지의 coherent radiation을 발생시킬 수 있는 개념의 장치이다. 이 장치에서 전자빔의 전류밀도는 출력되는 전자기파의 power와 직접적으로 관계하여 고출력 microwave 발생장치를 구성할 수 있다. 이번 실험에서는 일정한 국부적으로 형성된 plasma에 따른 강렬한 상대론적 전자빔의 전파효율의 향상을 관찰하였다.

• 전기의세계
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• v.20 no.5
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• pp.15-18
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• 1971

Up to now, there have been numerous investigations about the effect of diffusion on the wave propagation in gaseous plasmas, but not so much in semiconductor magnetoplasmas. However, currently, it becomes the centor of interest to work with the latter problem, and this paper deals with the dispersion equation including diffusion effect in the latter case to see how diffusion affects the equation in which diffusion term is neglected in the first place, and the analysis is based on the assumption that the plasma can be treated as a hydrodynamical fluid, since, from a macroscopic view point, the plasma interacting with a magnetic field can be considered as a magneto-hydrodynamical fluid, an electrically conducting fluid subjected to electromagnetic force, and the system is linear. The results of the relation and computation show that in the non-streaming case the diffusion terms appear in the equation as perturbation terms and the amplitude of the wave vector changes parabolically with the variation of the angular frequency and the longitudinal modes are observed.

• Journal of Korean Vacuum Science & Technology
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• v.3 no.1
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• pp.59-65
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• 1999

There has been an interest to develop an efficient, compact microwave device using field-emitter-arrays (FEA)-based cathode. Toe valuate the optimum device-efficiency in a compact size, the propagation properties of the premodulated electron beam for the FEA-based cathode is studied in detail by the computer simulation using a PIC code, MAGIC. For the premodulated electron beam whose phase of the energy leads the phase of the current by $\pi$/2, the amplitude of the downstream current modulation can be kept as high as the initial modulation level. Using the beam parameters with the beam voltage of 6kV and the current of 2.0A, 30% of efficiency is predicted when the quality factor of 800 is chosen. the device length is reduced about twice compared with that of the conventional device. The design of practical planar cathode is carried out to meet the minimum diameter of the electron beam as 0.5 mm.

• Asian-Australasian Journal of Animal Sciences
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• v.16 no.9
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• pp.1348-1354
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• 2003

The feeding value of high-oil corn fed to Taiwan Country (TC) chicken was examined by measuring apparent metabolizable energy (AME), growth performance, sexual maturity, carcass characteristics, and plasma pigmentation. In a completely randomized design, 870 sex-intermingled one-wk-old chicks were assigned to one of 30 floor pens, 29 birds per pen, and each pen randomly assigned to one of five dietary treatments. The experiment was ended when birds were 16 wk of age. The five dietary treatments varied in main fat sources, which were corn oil (CO), high-oil corn (HOC), lard (LRD), whole soybean (WSB) and yellow corn (YC), respectively. All the diets were formulated isonitrogenously, isocalorically, and of equal lysine and methionine contents except YC, in which equal amounts of YC replaced HOC. The results indicated that feed conversion in HOC was 8% higher (p<0.05) than YC whereas the calculated AME of HOC was only 3.5% to 4.0% higher than that of YC. No significant differences were observed in body weight, body weight gain, feed consumption, feed conversion ratio and ME efficiency for body weight gain among CO, HOC, LRD, and WSB. No significant differences existed in both skin and muscle pigmentation of breast among the five dietary treatments. No significance differences existed in plasma carotenoid content measured at various ages among the five dietary treatments except that birds fed with HOC had less (p<0.05) plasma carotenoids at 16 wk-old. The results indicate that if the price of high-oil corn is no more than 1.05 times that of yellow corn, the dietary cost per kg of body weight gain for TC chickens fed diets containing high-oil corn will be less, although their body weight may be lighter compared to chickens fed diets formulated with other fat sources.

• Korean Journal of Materials Research
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• v.10 no.7
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• pp.505-514
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• 2000

The carburizing behavior and fatigue properties of the plasma carburized low carbon Cr-Mo steel(0.176C-1.014Cr-0.387Mo) have been investigated. The effective case depth in plasma carburized steel increased up to 50% in comparison with that of gas carburizing, and this case depth increased with the increasing surface carbon content. With increasing time in plasma carburizing, the surface carbon content increased but its increasing rate decreased. Fatigue properties were studied in terms of microstructure, case depth, retained austenite and residual stress near the surface. The fatigue limit of the plasma carburized steel was higher than that of gas carburized one. The initiation of microcracks and initial crack propagation were retarded due to a relatively little surface and internal oxidation layer in plasma carburized steel. Fractography showed the crack initiated at the surface, and transgranular fracture at surface layer was more predominant in plasma carburized steel compared to that of gas carburized steel.